In mobile networks, such as a 3GPP (Third Generation Partnership Project) mobile network, various types of terminal devices may be used. For example, Machine Type Communication (MTC) terminal devices may be used in addition to conventional types of terminal devices, in the following also termed as user equipment (UE), such as mobile phones, smartphones, data modems, mobile computers, or the like. MTC terminal devices typically transmit and receive only small amounts of data, which may occur more or less infrequently, e.g., once per week to once per minute. MTC terminal devices may also be polled for data, resulting in an irregular pattern of data transmission. MTC terminal devices are typically assumed to be autonomous sensor devices, alarm devices, actuator devices, remote control devices, or the like, which communicate with application servers, rather than being used for communication by a human user. Hence, this type of communication may also be referred to as machine-to-machine (M2M) communication and the devices may be denoted machine devices (MDs). An application server may in turn configure the MTC terminal device and receive data from them. The application server may be within or outside the mobile network.
Considering the above, MTC terminal devices are typically characterized by a modest bit rate and sparse communication. MTC terminal devices may therefore be implemented with low-performance data transmission capabilities. Further, MTC devices typically need to be very energy efficient, since external power supplies may not be available and/or it may be practically or economically not feasible to frequently replace or recharge their batteries.
A known way of energy saving in a UE, which may also be applied to MTC devices, is to use Discontinuous Reception (DRX). By means of DRX, a UE can enter an energy efficient sleep mode when no data transmission is needed. In the sleep mode, receiver circuitry of the UE may be turned off. DRX can be applied in connected mode, but also in idle mode, in which the UE only receives paging information on certain paging occasions. The latter scenario may also be referred to as paging DRX or idle DRX. Paging information can be signaling to a terminal device to initiate a connection to a base station. Paging, i.e., the transmission of paging information, can be a process used by the mobile network to contact a terminal device which has no connection or association to a base station and whose location is known with an accuracy that may be less than a single cell.
According to 3GPP Technical Specification 36.304 V10.5.0, the paging DRX cycle is defined by paging configuration information, through parameters T and nB. The parameter T is defined as the minimum of the “defaultPagingCycle” Information Element (IE), transmitted to the UE by the mobile network, and a possible preconfigured UE specific DRX cycle length. The parameter nB is transmitted by the mobile network to the UE together with the “defaultPagingCycle” IE. The paging DRX cycle is divided into a sleep period and an active time, also referred to as active period. The active time essentially is equal to a paging occasion defined by the paging configuration information.
If a MTC terminal device, or other type of UE, has entered a new cell during the sleep period, it may first need to retrieve new paging configuration information before it is ready to receive paging information in the new cell. Otherwise the MTC terminal device or UE may fail to receive paging information transmitted at the beginning of the DRX active time or may even completely fail to receive the paging information transmitted at a certain paging occasion. This may become particularly significant if a long paging DRX cycle, e.g., with sleep periods of several minutes, hours or even longer is used. Long DRX sleep periods typically imply a greater probability of waking up in a new cell. Further, a missed paging occasion may result in a long delay in the order of another DRX sleep period until the next possibility of receiving the paging information. Similar problems may also occur if there is no cell change because the paging configuration may change also in within the same cell.
Accordingly, there is a need for efficiently transmitting paging information to terminal devices which apply DRX for receiving the paging information.